These inventions relate to a novel vacuum processing chamber and method for processing substrates. More particularly, this invention relates to a vacuum processing chamber and processing method in which deposition gasses are admitted and exhausted from the chamber.
Single substrate processing chambers for substrates such as silicon wafers, have been used for some time because among other reasons, the chamber volume can be minimized, contamination of the substrate can be reduced, and the process control increased such that yields can be improved. Further, vacuum systems have been developed, such as described in Maydan et al, U.S. Pat. No. 4,951,601, that allow several sequential processing steps to be carried out in a plurality of vacuum processing chambers connected to a central transfer chamber, so that several processing steps can be performed on a substrate without its leaving a vacuum environment. This can further reduce contamination of the substrates.
Other types of substrates are also processed in vacuum systems. For example, large glass substrates having active thin film transistors can be used as active matrix television and computer displays. Some glass substrates can be as large as a meter in length or longer. The basic methods and processing chambers, e.g., plasma enhanced chemical vapor deposition (PECVD), physical vapor deposition (PVD), etch chambers and the like, can be used for glass substrates in a manner similar to those used for depositing layers and patterning thin films on silicon wafers.
In conventional single substrate PECVD chambers, the substrate to be processed is typically supported by a heated susceptor and reaction gases are fed to the chamber via a gas dispersion plate mounted above and generally parallel to the substrate. The gas dispersion plate and susceptor can be connected across an RF source such that when power is turned on in the presence of a precursor gas, a plasma forms in the region between the gas dispersion plate and the substrate. Typically, the heated susceptor is movable to elevate the substrate to a desired position below the gas dispersion plate to improve the uniformity of deposition.
One deposition method provides a continuous flow of gasses through the chamber in which a first reaction gas is added to the flow, followed by a purge gas, a second reaction gas and again a purge gas. This sequence is cycled many times (typically, 25-200 cycles, depending upon the particular process) until a desired thickness is achieved. For example, one continuous flow process deposits a layer which is approximately 1 Angstrom thick each cycle and the cycle is repeated until approximately 25-200 Angstroms is deposited onto the substrate. During the deposition, the exhaust outlet of the chamber is kept substantially open to permit the continuous flow of the gas mixtures through the chamber.
Materials deposited in such continuous processes include tungsten, titanium, titanium chloride, and other materials which are suitable to be vaporized or evaporated and injected into a stream. In some deposition processes such as atomic layer deposition (ALD), each deposition gas is injected into the chamber in a relatively short pulse during each of the deposition cycles. For example, a deposition gas injection pulse may be on the order of a half second or less.
Another deposition method introduces a deposition gas into the chamber in which the exhaust outlet is sealed so that relatively high pressures of the deposition gas may be achieved in the chamber. This deposition method is considered to be noncontinuous in that the chamber admits a quantity of reaction gas and holds it until the desired deposition thickness has been achieved. The chamber exhaust outlet is then unsealed and opened and the deposition gas is purged from the chamber. The exhaust outlet valves tend to be relatively slow to open because the seals may need to decompress or may otherwise delay the opening of the outlet valve. Materials deposited in such non-continuous depositions include aluminum, for example, which may be deposited in a chamber atmosphere of several thousand p.s.i.
By manipulation of gas flows, temperatures, and pressure in the chamber maintained by a vacuum exhaust system, most of the particulates in the plasma region can be carried by the gases away from the susceptor and substrate and to the exhaust system. U.S. Pat. No. 5,582,866, which is assigned to the assignee of the present application, discloses a vacuum exhaust system which includes a plenum chamber connected to an exhaust port and vacuum pump. The plenum chamber is built into the lid so as to completely surround the gas dispersion plate and be above and surrounding the substrate periphery. A non-sealing, pressure-controlling throttle valve coupled to the exhaust port can control the flow of material from the chamber through the pump.
In one embodiment of the present inventions, an exhaust outlet in a vacuum processing chamber includes a nonsealing flow restrictor which can facilitate rapid opening and closing of the flow restrictor in some applications. Such a flow restrictor may be used in a variety of different chambers and deposition methods. It is believed that a nonsealing flow restrictor in accordance with the present invention is well suited to fast cycle deposition sequences such as atomic layer depositions (ALD).
Because the flow restrictor is a nonsealing flow restrictor, the conductance of the flow restrictor in the closed position may not be zero. However, the flow restrictor can restrict the flow of an exhaust gas from the chamber to permit the retention of sufficient processing gas in the chamber to deposit a film on the substrate or otherwise react with the substrate. In a preferred embodiment, the flow restrictor is a near sealing flow restrictor. After the desired film has been deposited or the processing of the substrate has been completed, the exhaust flow restrictor may be opened such that the flow restrictor conductance is significantly increased to a second, higher flow rate to facilitate exhausting residue gas from the chamber.
The closing and opening of the exhaust flow restrictor may be repeated as many times as needed to deposit additional layers onto the substrate until the desired thickness is achieved. In one embodiment, an atomic layer is deposited each cycle of the closing and opening of the exhaust flow restrictor. It is contemplated that different deposition materials may be alternately deposited as the deposition builds up onto the substrate.
A vacuum processing chamber in accordance with one embodiment comprises a plenum chamber coupled to an exhaust port and vacuum pump, in which plenum chamber is built into or adjacent to the lid so as to completely surround the substrate periphery. The near sealing exhaust flow restrictor when open couples the plenum chamber to the plasma processing region above the substrate. The near sealing exhaust flow restrictor, like the plenum, also surrounds the substrate. The flow restrictor passageway or passageways may be positioned around the substrate such that spent gases and particulates may be withdrawn from the plasma processing region in a desired fashion.
There are additional aspects to the present inventions. It should therefore be understood that the preceding is merely a brief summary of some embodiments and aspects of the present inventions. Additional embodiments and aspects of the present inventions are referenced below. It should further be understood that numerous changes to the disclosed embodiments can be made without departing from the spirit or scope of the inventions. The preceding summary therefore is not meant to limit the scope of the inventions. Rather, the scope of the inventions is to be determined by appended claims and their equivalents.